The present invention relates to a method of producing, with relative ease, a target formed of a sintering-resistant material of high-melting point metal alloy, high-melting point metal silicide, high-melting point metal carbide, high-melting point metal nitride or high-melting point metal boride, which has poor machinability. Specifically, the present invention relates to a target formed of a sintering-resistant material of high-melting point metal alloy, high-melting point metal silicide, high-melting point metal carbide, high-melting point metal nitride or high-melting point metal boride and its production method of inhibiting the generation of cracks during the target production and high power sputtering effectively. The present invention also relates to a sputtering target-backing plate assembly and its production method.
The term ‘high-melting point metal’ as referred to herein is 4B, 5B, 6B, 7B and 8 group metal of the Periodic Table of elements having a melting point of approximately 1700° C. or higher, and the term ‘high-melting point metal alloy’ herein is an alloy or intermetallic compound formed of the foregoing high-melting point metal. The high-melting point metal silicide, high-melting point metal carbide, high-melting point metal nitride or high-melting point metal boride as referred to herein is the ceramic of the foregoing high-melting point metal having a melting point of approximately 1700° C. or higher.
The usage of a sintering-resistant material of high-melting point metal alloy, high-melting point metal silicide, high-melting point metal carbide, high-melting point metal nitride or high-melting point metal boride is rapidly expanding; for instance, as various barrier films in a solid state device, as various electrode materials of a semiconductor capacitor and the like, as various hard coating materials of cutting tools and the like.
For deposition based on the sputtering method, direct current (DC) sputtering, radio frequency (RF) sputtering or magnetron sputtering is used from the perspective of operability and stability of the film.
Formation of a film according to the sputtering method is performed by physically colliding accelerated positive ions such as Ar ions to a target placed on a cathode, emitting a material configuring the target based on the momentum exchange caused by the collision energy, and laminating a film having roughly the same composition as the target material on the substrate of the opposing anode.
The coating method based on the foregoing sputtering method is characterized in that it is able to form films in a wide range; for instance, thin films of Angstrom units to thick films of several tens of μm, with a stable deposition speed by adjusting the treatment time, power supply, and other conditions.
When depositing high-melting point metal alloy or high-melting point metal ceramic via sputtering, a requisite condition is to produce a sputtering target with powder metallurgy. However, there is a problem in that machining is difficult since the material is hard and brittle. When placing a target formed of high-melting point metal alloy or high-melting point metal ceramic on a sputtering device, it is necessary to bond such target to a backing plate, but there is an additional problem in that this processing of bonding is in itself difficult.
Although there are demands for performing ionization during the sputtering and performing such sputtering with high power, there is a problem in that, with a target that is solder-bonded using a brazing filler material or the like, the target will crack due to the melting or the like of the brazing filler material.
Conventionally, numerous types of sputtering target materials have been used, and some are easy to produce and others are difficult to produce like the present invention. Various schemes have been devised and reasonable production methods have been proposed, and some examples are described below.
For instance, Patent Document 1 proposes technology of using an insert material having a lower melting point than the target material upon bonding a target having a melting point of 1000° C. or higher and a backing plate, and solid-phase diffusion bonding the insert material and the target, and the insert material and the backing plate, respectively. Although this production method is in itself extremely effective, it is necessary to prepare a plate-shaped target material in advance.
Even if this technology is applied to the production of a high-melting point metal alloy or high-melting point metal ceramic target and the target is prepared in a plate shape in advance, there is a problem in that the preparation for bonding the target with the backing plate cannot be made since it is not possible to perform crude processing to the bonding interface of the target. Accordingly, there is a problem in that this technology cannot be applied to the production of a high-melting point metal alloy or high-melting point metal ceramic target.
Patent Document 2 discloses technology of arranging a brazing filler material and a buffer material between a target and a cooling member (backing plate), and forming a deposition or plated layer formed of a material for improving the wettability on the bonding interface of the target.
Nevertheless, with a target that is a high-melting point material and which is to be sputtered at high power, the bonding method using a brazing filler material having a low melting point cannot be adopted since it may cause an accident where such brazing filler material falls off during the sputtering.
Patent Document 3 proposes technology of performing diffusion bonding or hard soldering via a metal insert material, which has thermal expansion that is smaller than a copper plate, between a graphite plate and the copper plate. This technology also entails the problems encountered in Patent Documents 1 and 2 described above, and cannot be applied to the production of a high-melting point metal alloy or high-melting point metal ceramic target.
Patent Document 4 proposes technology of providing tungsten or its alloy powder on molybdenum or its alloy powder, additionally forming a coating layer of molybdenum powder thereon, subjecting this to hot forging, and ultimately cutting and eliminating the coating layer. This technology is for use as an X-ray tube target material and relates to a special production method, but since it does not in any solve the problem regarding the bonding of the target to the backing plate, it cannot be applied to the production of high-melting point metal alloy or high-melting point metal.
Patent Document 5 proposes technology of placing a titanium backing plate and tungsten-titanium powder in a vacuumed can and simultaneously performing sintering and bonding based on HIP (Hot Isostatic Pressing) when manufacturing a sputtering target by bonding tungsten-titanium to a titanium backing plate. This technology is inefficient since the use of a vacuumed can is troublesome.
Moreover, although it is desirable to use a copper or copper alloy backing plate from the perspective of cooling efficiency, if the difference in the melting point between the target and the backing plate is significant as in this case, there is a problem in that the method cannot be applied since the bonding will be difficult.
Patent Document 6 proposes forming a titanium intermediate layer between a target and a backing plate upon bonding a cobalt target plate and an aluminum or copper backing plate based on hot press or HIP. Nevertheless, in this case, it is a problem in that this is possible only when the target material itself has workability, and cannot be applied to the production of a high-melting point metal alloy or high-melting point metal ceramic target.
Patent Document 7 describes improving the economic efficiency by diffusion bonding a nonmagnetic plate to a magnetic material target, and reducing the amount of magnetic material to be used, as well as providing mechanical strength to the magnetic material in order to prevent the generation of warpage and cracks during the machining process. This method aims to make the magnetic plate thinner, and, after preparing a magnetic plate in advance, a nonmagnetic plate to become the reinforcing plate is diffusion bonded thereto. This technology does not overcome the problem of bonding highly brittle sintering materials.
From a comprehensive standpoint, it is extremely difficult to product a target formed of high-melting point metal alloy or high-melting point metal ceramic with the conventional technology, and it was not possible to overcome the problem of target cracking during the production or sputtering.    [Patent Document 1] Japanese Patent Laid-Open Publication No. H6-108246    [Patent Document 2] Japanese Patent Laid-Open Publication No. H5-25620    [Patent Document 3] Japanese Patent Laid-Open Publication No. S62-202732    [Patent Document 4] Japanese Patent Laid-Open Publication No. S63-169307    [Patent Document 5] U.S. Pat. No. 5,397,050    [Patent Document 6] U.S. Pat. No. 6,071,389    [Patent Document 7] Japanese Patent Laid-Open Publication No. H5-86460